A previously proposed method of depositing Germanium Carbide involves the use of glow discharge techniques. Such techniques are disadvantageous in that they require high substrate temperatures, i.e. above 500.degree. Centigrade, and hydrocarbon gasses, and deposition of the Germanium Carbide is relatively slow. Due to the high substrate temperatures, the Germanium Carbide deposited by such methods is subjected to high stresses as a result of differing coefficients of expansion between the substrate on which the Germanium Carbide is deposited and the Germanium Carbide itself. When the Germanium Carbide is subjected to such stresses, the infra-red absorption coefficient of the Germanium Carbide is increased. Further, the unwanted stress imposes limitations on the thickness of the Germanium Carbide which can be usefully deposited.